The present invention relates generally to devices that are mounted on vehicles to operate safety units associated with the vehicle, such as crossing arms, stop signs and the like which are mounted on school buses for selective movement between a retracted or passive position adjacent the school bus and an extended or active position at which the safety unit extends outwardly from the bus to perform a safety function.
It is, of course, well known that children, particularly young children, who are transported in school buses are vulnerable to accidents involving the school bus or the children themselves during the time they are leaving or approaching the school bus, and it is therefore common practice to provide school buses with safety units that are designed to reduce the risk of such accidents.
One familiar safety unit that is almost universally found on school buses is the octagonal stop sign that is usually mounted on one side of the school bus, and that is movable from a normal retracted position along the side of the school bus to an extended position projecting outwardly from the side of the bus to warn other motorists that children are leaving or approaching the school bus so that such motorists can stop all movement of their vehicles until the children have safely boarded the bus or cleared the area after leaving the bus. Typical stop sign safety devices of this type are disclosed in Latta U.S. Pat. Nos. 4,138,668; 4,339,744; and 4,559,518.
Another familiar safety unit frequently found on school buses is a crossing arm that is usually mounted on the front bumper of the school bus and that is arranged for pivotal movement from a first retracted or passive position at which the generally lengthy crossing arm extends along and adjacent the bumper to a second active position at which it extends outwardly and generally perpendicular with respect to the bumper, thereby providing a barrier that forces children to walk in a path well away from the front bumper of the school bus so that the driver of the school bus can readily see the children and avoid moving the bus until they have cleared the area in front of the bus. The construction and operation of crossing arms of this type are disclosed in greater detail in Latta U.S. Pat. No. 4,559,518, Wicker U.S. Pat. No. 4,697,541 and Runkle U.S. Pat. No. 3,153,398.
As discussed in the above-identified prior art patents, the actuating devices for moving the safety units between their retracted and deployed or extended positions may be vacuum (or air) operated, or they may be electrically operated, and such actuating devices are generally designed to stop movement only at the retracted and deployed positions. However, since the safety units, at their deployed positions, are extending outwardly and generally perpendicularly from the school bus, they invite the attention of children, and others, and offer a tempting target to be pushed away from such extended position by the children passing by the extended safety unit. Also, even in their retracted positions, the safety units present a temptation for children to pull them outwardly from such retracted position. Obviously, if the actuating device for the safety unit included only a rigid drive connection between the operating mechanism (e.g. electric motor) and the movable safety unit, any such manual pushing or pulling force applied directly to the safety unit could damage or even destroy the operating mechanism of the actuating device.
To overcome this problem, it is now common practice to provide safety unit actuating devices with a double-acting hinge construction of the type generally disclosed in Latta U.S. Pat. No. 4,138,668 that includes relatively heavy coil springs that are arranged to resist any manual movement of the safety unit from its set position, and, if a manual force is applied to the safety unit of sufficient magnitude to move the safety unit from its set position, the springs will return the safety unit to its original set position. Also, there is another known hinge device that accomplishes generally the same function as the aforesaid double-acting hinge by utilizing a combination of a biasing spring and cam surface arrangement, whereby manual movement of the safety unit causes the cam to move along a cam surface until the safety unit is released, and the spring then returns the safety unit to its extended position. The cam surface has a configuration such that if the safety units moved within a predetermined range from its extended position, it will return to its extended position, but if it is moved beyond such predetermined range and toward its retracted position, it will be moved by the spring to the retracted position rather than returned to the extended position. An example of this type of hinge device is disclosed in U.S. Pat. No. 4,766,413.
While the aforesaid hinge arrangements serve their intended purpose of permitting some manual movement of the safety unit, usually without damage to the actuating device, and returning the safety unit to its original position after it has been manually moved, these arrangements still have some disadvantages. First, the springs used to return the safety unit to its original position must be relatively strong to accomplish this purpose, and, as a result, when a safety unit is manually moved a considerable distance from one of its set positions (e.g. the deployed position) and released, the return movement caused by the springs has a whipping action that can present an unsafe condition if a child is in the path of the safety unit during its return. This problem is more pronounced in conjunction with crossing arms because of the considerable extending length of the arm. Additionally, the construction of the hinge arrangement, and the corresponding drive unit that includes crank arms, connecting arms and related mechanisms, add to the cost of manufacturing the devices. Finally, even with a break-away type hinge arrangement, there can be circumstances under which the direct drive system from an electrical drive motor can be misused in such a manner as to strip the motor or otherwise damage the drive arrangement.
The present invention provides an actuating device for safety units which is more reliable and safer than known devices of this type, and it provides a construction that is less complicated and less expensive than known constructions.